Rockwell Automation 1756-OF8I ControlLogix Eight-channel Isolated Analog I/O Modules - Manual (Page 31)

Rockwell Automation Publication 1756-UM540A-EN-P - May 2014 31
ControlLogix Isolated Analog I/O Module Features Chapter 2
Compatible Keying
Compatible Keying indicates that the module determines whether to accept or
reject communication. Different module families, communication adapters, and
module types implement the compatibility check differently based on the family
capabilities and on prior knowledge of compatible products.
Compatible keying is the default setting. Compatible keying lets the physical
module accept the key of the module configured in the software, provided that
the configured module is one the physical module is capable of emulating. The
exact level of emulation required is product and revision specific.
With Compatible keying, you can replace a module of a certain Major Revision
with one of the same catalog number and the same or later, that is higher, Major
Revision. In some cases, the selection makes it possible to use a replacement that
is a different catalog number than the original. For example, you can replace a
1756-CNBR module with a 1756-CN2R module.
Release notes for individual modules indicate the specific compatibility details.
When a module is created, the module developers consider the module’s
development history to implement capabilities that emulate those of the previous
module. However, the developers cannot know future developments. Because of
this, when a system is configured, we recommend that you configure your module
by using the earliest, that is, lowest, revision of the physical module that you
believe will be used in the system. By doing this, you can avoid the case of a
physical module rejecting the keying request because it is an earlier revision than
the one configured in the software.
EXAMPLE In the following scenario, Compatible keying prevents I/O communication:
The module configuration is for a 1756-IB16D module with module revision
3.3. The physical module is a 1756-IB16D module with module revision 3.2. In
this case, communication is prevented because the minor revision of the
module is lower than expected and.cant be incompatible with 3.3.
Module Configuration
Vendor = Allen-Bradley
Product Type = Digital Input Module
Catalog Number = 1756-IB16D
Major Revision = 3
Minor Revision = 3
Physical Module
Vendor = Allen-Bradley
Product Type = Digital Input Module
Catalog Number = 1756-IB16D
Major Revision = 3
Minor Revision = 2
Communication is prevented
ANALOG INPUT
ST 0 1 2 3 4 5 6 7 ST 8 9 10 11 12 13 14 15 O
K CAL
OK
OK FORCE SD RUN
Logix5575
RU N REM PROG
DC INPUT DC INPUT
FLT 8 9 10 11 12 13 14 15
ST 0 1 2 3 4 5 6 7
ST 8 9 10 11 12 13 14 15 O
K FLT 0 1 2 3 4 5 6 7
DIAGNOSTIC